Surge control device for centrifugal compressors



Feb. 26, 1963 R. s. GRIFFIN@ 3,079,121 suRGE CONTROL DEVICE FOR CENTRIFUGAL coMPREssoRs Filed June 11, 1957 hitates s This invention pertains to centrifugal compressors, and more particularly to a surge con-trolling device for a centrifugal compressor.

Some centrifugal compressors have a tendency to surge or hunt when operating under low load conditions. The surging or hunting of a centrifugal compressor manifests itself in a bacidlow of lluid into the compressor impeller and adversely atects the eicient operation of the unit, Aand in extreme conditions, may actually damage the compressor.

This invention would solve the above problems by providing a by-pass valve to by-pass a portion of the compressor flow from the discharge side back to the linlet side to increase the load on the compressor when the compressor tends to surge, and thus prevent surging. The by-pass valve is operated by a pneumatic actuator which is responsive to two pressures which indicate the rate of liow from the discharge of the compressor. ri`hus, the 1oy-pass valve may maintain a predetermined minimum rate of flow through the 4compressor regardless of the actual load on the compressor. The maintaining of a predetermined minimum rate of iiow thro-ugh the compressor eliminates any tendency of the compressor to surge or hunt.

Accordingly, it is the principal object of this invention to provide a novel by-pass valve for a centrifugal com; pressor which is operated so as to maintain a minimum ilow through the compressor.

Another object oi this invention is to provide a novel design for a by-pass valve in which the by-pass valve, the actuator used for positioning the by-pass valve, and the control valve which controls the admission of lluid to the actuator are all mounted in a common housing.

Still another object or" this invention is to provide a unique by-pass valve which is operated by a single-ended actuator which, in turn, is ope-rated by the tluid being circulated by the compressor.

rfhese and other objects and advantages of this invention will be more apparent to those skilled in the art from the following detailed description of a preferred embodiment when taken in' conjunction with the 'accompanying drawing showing:

A by-pass valve constructed according .to this invern tion installed on a centrifugal compressor designed to handle vapor cycle refrigerante.

Referring to the drawing, there is shown, incorporated in a conventional vapor cycle refrigeration system consisting of a compressor, a condenser, an expansion valve I and an evaporator, a by-pass valve Sti) having an inlet il connected, by way ot illustration, to the refrigeration system near the bottom, but above the liquid refrigerant level, of the condenser i2. lt is to be understood, howover, that the by-pass valve would operate eiectively to t into the scroll-shaped chamber 2G. From the scroll-.

arent Patented Feb. 25, i953 shaped chamber the liuid ows through the discharge conduit 2l of the compressor to the condenser l2 of the refrigeration system. Mounted in the discharge conduit 2l of the compressor is a sensing probe 22 which senses two pressures whose difference is a measure of the rate olf ow through the discharge 21. The two pressures ensed by the probe 22 are applied to the opposite sides of the diaphragm which operates the flow control or pilot valve 23. The liow control valve 23, in turn, controls the amount of pressurized fluid admitted to the actuator 24 which is used to position the by-pass valve 10.

The by-pass valve has a tubular-shaped valve body formed from a tubular section 30 which is secured to Ian end cover 3l by means of a plurality of circumferentially spaced cap screws 32. A valve seat insert is positioned in the outlet or open end of the tubular section 36 of the valve body and has a valve seat 34 form on its extreme end. A valve disc 35 is disposed so as to engage the valve seat 34 and is provided with a valve stem 36 which extends through a valve stem guide 40 located centrally in the tubular section 30. The valve disc 35 and the valve stem 35 may be formed as a single piece unit or may be formed of separate pieces which are fastened together to form a unitary structure. The valve stem guide 4i) is supported by a plurality of ciroumferentially spaced radial webs 41 extending from the inner sunfa'ce of the tubular section 3b. The inletopening l1 of the by-pass valve is formed in the wall of the tubular section 34?.

The right-hand end of vthe valve stern 36 is secured to `a diaphragm assembly 42 by means of a nut 45 which threads over the end of the valve stem. The nut i3 secures the diaphragm assembly against a washer 44 which bears against a shoulder formed on the end of the valve stern 36. The diaphragm assembly consists of a diaphragm d5, the outer edges of which are secured between the mating flanges or" the tubular section 3i) and top cover 3l and two diaphragm support plates do which are fastened together by any desired means such as a plurality of circumferentially spaced rivets Sil. A compression spring ill is mounted on the left-hand side of the diaphragm assembly 42 and reacts against the radial webs il to force the diaphragm assembly to the right to close the by-pass valve. A passageway 52 is formed in the center of the valve ste-m 36 to connect the right side of the diaphragm assembly 42 with the inlet of the compressor. A portion of the passageway 52 is reduced in size to form a ow control orifice means 53.

The above described construction thus provides a poppet type by-pass valve which is positioned or controlled by means of a single-ended iluid operated actuator. The actuator is spring biased in a direction to close the puppet Valve and is opened by admitting pressurized iiuid from the discharge of the compressor to the dgt-hand side Aof the diaphragm assembly d2, as will be described below.

A closed chamber is formed in the end cover 3i of the valve body by means of a rigid radial wall efiiwhich is retained in position by means of a snap ring 55 which lits in a cooperating groove formed on the inner surface of the end cover 31. The outer sunface of the radial wall is sealed to the inner surface of the end cover by means of an O-ring Sti which tits in a cooperating groove formed on the outer surface of the radial wall. The closed chamber is divided into two separate sections 67 and 68 by a second diaphragm Gli, the outer edge of which is retained between the end of `the radial wall Sli and a shoulder formed on the end cover 3i. The center portion of the diaphragm 6l! vis retained between two diaphragm plates 6i and 62 which are fastened together by means of Ia plurality of circuniferentially spaced rivets 63. The diaphragm plate 52, in addition, acts as a Valve 4to open and close the end of a passageway o'formed in a tubular member 64, as will be explained more itully below. A light compression spring is mounted in the left section 68 of the closed chamber and reacts against the radial wall 54 to urge the diaphragm d@ to .the right.

The tubular member 64- threads into a central opening in the radial wall 54 and is locked in position by means of a locking nut 66 which threads over the left-hand end of the tubular member 64, The tubular member 64 is provided with a restricted passageway 65 in its center which acts as a llow control orifice. The position of the tubular member is adjusted so that its right-hand end 7l. is slightly spaced from the diaphragm plate 62 under n'ormal operating condtiions, as will be expalined more fully below.

Two passageways 80 and S1 are formed in .the pressure sensing probe Z2. The ends of the passageways Si) and 81 are turned at right angles to the main axis of the probe so that the open end of passageway 8d faces in the opposite direction of the -ow through the discharge 21 While the open end of the passageway Si faces in the same' direction as the iiow through the discharge 2i. The passageway 81 could altern-ately be turned at right angles to the passage 8) so that it senses only the static pressure in the discharge conduit 21. The iiuid pressure sensed by the open ends of the passa-geways 80 and 81 are sup` plied to the two sections 67 and 68 off `the closed chamber by means of tubes S2 and 83, respectively. The tubes 82 and 83 are connected to passageways 84 and 85 formed in the end cover 31 of the by-pass valve and opening into the two sections 67 and 68, respectively.

When the compressor of the above invention is operated, it will draw fluid through the inlet opening 14 and discharge it radially outward into the scroll-shaped chamber 20. From the scroll-shaped chamber 20, the iiuid flows out the discharge 21 to the condenser 12. When the compressed iiuid ilows by the sensing probe 22, the passageway 80 will sense a fiiuid pressure equal to the discharge pressure plus a portion of the velocity head, while the passageway 81 will sense a pressure equal to the discharge pressure minus a portion of the velocity head. Thus, under normal operating conditions, the passageway 80 will sense a tluid pressure which exceeds the pressure sensed by the passageway S1. The higher Vpressure of the two pressures is applied to the right-hand surface of the diaphragm 6), thus urging it towards the left so that the plate 62 will close the end 71 of the passageway 65 formed in the tubular member 64. When the pasageway 65 is closed, no fluid pressure can flow through the passageway 65 into the chamber formed by the diaphragm 45 and Ithe radial wall 54. Any small amount of pressurized iiuid which leaks through the passageway 65 will quickly be vented by the passageway 52 formed in the valve stem 36, hence the pressure in' the chamber formed by the diaphragm 45 and the radial wall 54 will be close to .that of the compressor inlet. Thus, under normal operating conditions, the spring 51 will hold the valve disc 35 in Contact with the valve seat 34 to prevent any iiow from the condenser 12 back to the suction inlet 14 of the compressor.

It is to be noted that the pilot valve 23 is actuated in response to small changes in diierential pressure to admit pressurized fluid to the right-hand side of diaphragm assembly 42. However, the admission of uid pressure into the chamber formed by the diaphragm 4S and the radial wall S4 creates a comparatively large difieren-tial across the diaphragm assembly 42 as the pressure of the iiuid acting on the valve disc 35 cancels the pressure of the iiuid acting on an equal area o the left-hand side of the diaphragm assembly 42. Thus a small change in the diierential in the pressures in passageways 80 and Si will produce a comparatively large force to positively actuate the valve disc 35.

When the iiow through the discharge 2l of the compressor is reduced, which would signal the approach to compressor surge conditions, the fluid pressures sensed by the open ends of the passageways Sil and 8i will be closer to equality. When the llow through the compressor discharge 2i tends to fall below the predetermined minimum ile-w for which the by-pass valve l@ is set, the spring '7d will lift the diaphragm 61% and plate 62 from the end 71 of the tubular member 642- to open the passageway 65. Pressurized iiuid from the compressor discharge will then flow into the chamber formed by the diaphragm 45 and the radial wall 54. When the pressure of the fluid acting on the right-hand side of the diaphragm 45 is suiiicient to overcome the force of the spring 5i and the net pressure of the fluid acting on the left-hand side of the diaphragm the valve disc 35 will be lifted oit the valve seat 34-, thus opening the by-pass valve to by-pass -liuid directly from the condenser 12 back to the suction inlet t4 of the compressor. As long as the flow of fluid through the discharge conduit 21 tends to fall below the predetermined set minimum the valve disc 3S will modulate and the additional tluid which is added to the amount being circulated by the compressor will prevent the tiow through the discharge 21 Vfrom decreasing below the predetermined minimum and thus eliminate any tendency of the compressor to surge. When the flow through the discharge 21 exceeds the predetermined minimum, the pressure sensed from the passageways 86 and 81 is suiciently unbalanced so that the diaphragm e!) will be forced to the left and the plate 62 will close oil the end of the restricted passageway 65 in the tubular member 64 and the valve 35 will close.

The restricted passageway 65 should be of sufficient size so lthat when it is uncovered it can admit more ilnid into the chamber formed by the diaphragm 4S and the radial wall 54 than can be vented through the ilow control oriiice 53 in the passageway 52. Also, the force of the spring '7d lshould be chosen so that it will maintain the predetermined minimum llow through the discharge 21 of the compressor. The minimum ow through the compresser may also be varied by adjusting the position of the tubular member 6e in relation to the diaphragm plate 62. The maintaining of a predetermined minimum ow through the discharge 21 will eliminate any tendency of the compressor to surge. In addition to the above features, the -by-pass valve of this invention utilizes the pressure of the fluid being circulated by the compressor to operate the actuator which is used to position the by-pass valve. This eliminates the need for separate sources of pressurized iiuid for operating the valve. Also, all of the operating members of the by-pass valve are mounted on a common axis iu a unitary housing which results in a simple and compact structure.

While the above description relates to the preferred embodiment of this invention, various modifications and improvements can 'be made without departing from its broad spirit and scope.

I claim:

l. A surge control device comprising: a by-pass valve including a tubular valve body having an inlet connection for by-pass iluid, said tubular valve body being closed at one end and open at the other end; a valve member in the open end of said tubular valve body arranged to control ow of by-pass fluid through said by-pass valve; a tirst diaphragm having its peripheral portion attached to the sides of said tubular Valve body; a valve stem fastened at one end to said valve member and extending into said tubular valve body, the other end of said valve stem being secured to said Iirst diaphragm; a restricted passageway formed in said valve stem and connecting one side of said iirst diaphragm with a zone of lower pressure; a rst spring disposed in said tubular valve body to urge said first diaphragm in a direction to close said valve mem-ber; a rigid wall mounted in said tubular valve body parallel to and axially spaced from said rst diaphragm to form a irst chamber, said diaphragm being arranged to exclude by-pass huid from said rst chamber, said Vrigid wall in combination with the closed end of said tubular valve body forming a second chamber; a second diaphragm having its peripheral portion attached to the sides of said valve body and dividing said second chamber into two sections; a valve seat formed on said rigid wall, said valve scat having passage means including a restricted opening to permit fluid communication between one of said sections and said first chamber, one end of said passage means being located adjacent one surface of said second diaphragm; a second spring disposed in said second chamber to urge said second diaphragm away from the said one end of said passage means; means adapted to sense a first fiuid pressure and a second fiuid pressure; and conduit means for connecting said first and second fluid pressures to the opposite sections of said second chamber, said second diaphragm modulating in response to the forces acting on opposite sides thereof so that one side of said second diaphragm coacts with said valve seat to open and close the passage means, thereby controlling the fiow of said sensed fluid through said restricted opening into said first chamber to operate said valve member.

2. A surge control device comprising: a by-pass valve including a tubular valve body having an inlet connecF tion for by-pass fiuid, said tubular valve body being closed at one end and open at the other end; a valve member in the open end of said tubular valve body arranged to control fiow of yby-pass fiuid through said by-pass valve; a first diaphragm having its peripheral portion attached to the sides of said tubular valve body; a valve stem fastened at one end to said valve member and extending into said tubular valve body, the other end of said valve stern being secured to said first diaphragm; a restricted passageway formed in said valve stem and connecting one side of said first diaphragm with a zone of lower pressure; a first spring disposed in said tubular valve body to urge said first diaphragm in a direction to close said valve member; a rigid wall mounted in said tubular Valve body parallel to and axially spaced from said first diaphragm to form a first chamber, said diaphragm being arranged to exclude by-pass fiuid from said first chamber, said rigid wall in combination with the closed end of said tubular valve body forming a second chamber; a second diaphragm having its peripheral portion attached to the sides of said valve body and dividing said second chamber into a first section and a second section; a tube extending through the rigid wall and terminating in the first section; a restricted passageway through the tube communicating between the first section and the first chamber; a second spring disposed in the second chamber to urge said second diaphragm away from the end of said tube; means for adjusting the tube longitudinally relative to the rigid wall; means adapted to sense a first iiuid pressure and a second fiuid pressure; and conduit means for connectino said first and second fiuid pressures to the opposite sections of said second chamber, said second diaphragm modulating in response to the forces acting on opposite sides thereof so that one side of said second diaphragm coacts with the end of said tube to open and close the passageway therethrough, thereby controlling the fiow of sensed fluid into said first chamber to operate said valve member.

3. A surge control device comprising: a by-pass valve including a tubular valve body having an inlet connection for by-pass uid, said tubular valve body being closed at one end by a cap and open at the other end; said valve body and said cap forming a joint therebetween; a valve member in the open end of said tubular valve body arranged to control fiow of by-pass fiuid through said by pass valve; a rst diaphragm having its peripheral portion clamped in the joint between the cap and said tubular valve b-ody; a valve ste-m fastened at one end to said valve member and extending into said tubular valve body, the other end of said valve stem being secured to said first diaphragm; a restricted passageway formed in said valve stem and connecting one side of said first diaphragm with a zone of lower pressure; a first spring disposed in said tubular valve body to urge said first diaphragm in a direction to close said valve member; said cap having an internal bore closed at one end by an end wall portion of the cap; a rigid wall in said bore parallel to and axially spaced from said first diaphragm to form a first chamber, said diaphragm being arranged to exclude by-pass iiuid from said first chamber, said rigid wall in combination with the end wall of said cap forming a second chamber; a second diaphragm having its peripheral portion clamped between the rigid wall and said end wall and dividing said second chamber into a first section and a second section; means securing the rigid wall in position in said bore; a tube extending thro-ugh the rigid wall and terminating in the first section; a restricted passageway through the tube communicating between the first section and the first chamber; a second spring disposed in the second chamber to urge said second diaphragm away from the end of said tube; means for adjusting the tube longitudinally relative to the rigid wall; means adapted to sense a first fluid pressure and a second fluid pressure; and conduit means for connecting said first and second fluid pressures to the opposite sections of said second chamber, said second diaphragm modulating in response to the forces acting on opposite sides thereof so that one side of said second diaphragm coacts with the end of said tube to open and close the passageway therethrough, thereby controlling the fiow of sense-d uid into said first chamber to operate said valve member.

References Cited in the file of this patent UNITED STATES PATENTS Re. 14,230 Earl Dec. 12, 1916 1,052,172 Rateau Feb. 4, 1913 1,110,864 Banner Sept. 15, 1914 1,685,205 Stein Sept. 25, 1928 1,803,660 Swartwout May 5, 1931 2,309,848 King Feb. 2, 1943 2,414,322 Mock Jan. 14, 1947 2,470,565 Loss May 17, 1949 2,562,615 Huber July 31, 1951 2,583,006 Niesemann lan. 22, 1952 2,637,946 Parks May 12, 1953 2,661,145 Heineman Dec. l, 1953 2,732,852 Lauck Jan. 31, 1956 2,751,923 Towler et al. June 26, 1956 2,771,265 Woods Nov. 20, 1956 2,786,420 Kenny Mar. 26, 1957 FOREIGN PATENTS 286,965 France of 1899 

1. A SURGE CONTROL DEVICE COMPRISING: A BY-PASS VALVE INCLUDING A TUBULAR VALVE BODY HAVING AN INLET CONNECTION FOR BY-PASS FLUID, SAID TUBULAR VALVE BODY BEING CLOSED AT ONE END AND OPEN AT THE OTHER END; A VALVE MEMBER IN THE OPEN END OF SAID TUBULAR VALVE BODY ARRANGED TO CONTROL FLOW OF BY-PASS FLUID THROUGH SAID BY-PASS VALVE; A FIRST DIAPHRAGM HAVING ITS PERIPHERAL PORTION ATTACHED TO THE SIDES OF SAID TUBULAR VALVE BODY; A VALVE STEM FASTENED AT ONE END TO SAID VALVE MEMBER AND EXTENDING INTO SAID TUBULAR VALVE BODY, THE OTHER END OF SAID VALVE STEM BEING SECURED TO SAID FIRST DIAPHRAGM; A RESTRICTED PASSAGEWAY FORMED IN SAID VALVE STEM AND CONNECTING ONE SIDE OF SAID FIRST DIAPHRAGM WITH A ZONE OF LOWER PRESSURE; A FIRST SPRING DISPOSED IN SAID TUBULAR VALVE BODY TO URGE SAID FIRST DIAPHRAGM IN A DIRECTION TO CLOSE SAID VALVE MEMBER; A RIGID WALL MOUNTED IN SAID TUBULAR VALVE BODY PARALLEL TO AND AXIALLY SPACED FROM SAID FIRST DIAPHRAGM TO FORM A FIRST CHAMBER, SAID DIAPHRAGM BEING ARRANGED TO EXCLUDE BY-PASS FLUID FROM SAID FIRST CHAMBER, SAID RIGID WALL IN COMBINATION WITH THE CLOSED END OF SAID TUBULAR VALVE BODY FORMING A SECOND CHAMBER; A SECOND DIAPHRAGM HAVING ITS PERIPHERAL PORTION ATTACHED TO THE SIDES OF SAID VALVE BODY AND DIVIDING SAID SECOND CHAMBER INTO TWO SECTIONS; A VALVE SEAT FORMED ON SAID RIGID WALL, SAID VALVE SEAT HAVING PASSAGE MEANS INCLUDING A RESTRICTED OPENING TO PERMIT FLUID COMMUNICATION BETWEEN ONE OF SAID SECTIONS AND SAID FIRST CHAMBER, ONE END OF SAID PASSAGE MEANS BEING LOCATED ADJACENT ONE SURFACE OF SAID SECOND DIAPHRAGM; A SECOND SPRING DISPOSED IN SAID SECOND CHAMBER TO URGE SAID SECOND DIAPHRAGM AWAY FROM THE SAID ONE END OF SAID PASSAGE MEANS; MEANS ADAPTED TO SENSE A FIRST FLUID PRESSURE AND A SECOND FLUID PRESSURE; AND CONDUIT MEANS FOR CONNECTING SAID FIRST AND SECOND FLUID PRESSURES TO THE OPPOSITE SECTIONS OF SAID SECOND CHAMBER, SAID SECOND DIAPHRAGM MODULATING IN RESPONSE TO THE FORCES ACTING ON OPPOSITE SIDES THEREOF SO THAT ONE SIDE OF SAID SECOND DIAPHRAGM COACTS WITH SAID VALVE SEAT TO OPEN AND CLOSE THE PASSAGE MEANS, THEREBY CONTROLLING THE FLOW OF SAID SENSED FLUID THROUGH SAID RESTRICTED OPENING INTO SAID FIRST CHAMBER TO OPERATE SAID VALVE MEMBER. 